DE2427592B2 - Oscillator circuit - Google Patents

Description

The invention relates to an oscillator circuit having a first and second voltage supply line cycle time capacitor connected in series to a charging resistor and a comparator, which is connected to a first control connection is connected to the clock time capacitor and to its second control connection with a Threshold voltage is applied to a control signal on the output side as a function of. the To supply voltage at the cycle time capacitor when a certain level is reached.

Oscillator circuits, especially in the form of sawtooth oscillators, use to determine the frequency

ίο mung ÄC networks. Oscillators of this type are often used in television receivers in deflection stages as clock circuits and as decoder circuits for stereo FM receivers. For some of these applications it is desirable that the frequency of the oscillator output signal remain stable even when there are fluctuations in the power supply and temperature changes. The frequency of the oscillator signal should only depend on changes in a control signal. Such oscillator circuits, especially for the horizontal deflection stage of television receivers or the decoder stage for stereo receivers, should be compatible with monolithically integrated phase detectors, which require that a certain voltage and impedance be maintained at the output of the oscillator stage. Such phase detectors supply a control signal for the synchronization of the oscillator output signal with a received clock signal.
There are known oscillator circuits which are suitable for many applications, but which prove to be disadvantageous if they are to be used in a system with a monolithically integrated phase tracking loop. Such known oscillator circuits require three different Potentialrii levels in order to be able to be operated optimally. However, since only two potential levels are usually easily available, it is necessary to provide further active and passive circuit components in the monolithic structure of the oscillator in order to create a third potential level. These additional circuit components not only take up additional space on the die, but also add to the heating and the increased likelihood of failure, since additional circuit components affect both the economics of manufacture and the reliability of the circuit. It is also known that such oscillator circuits as sawtooth oscillators depend in an undesirable manner on the temperature and experience a change in the sawtooth frequency as a function of the temperature. When such sawtooth oscillators are used in the horizontal deflection system of television receivers, the sawtooth has a relatively long rise time compared to the fall time associated with the beam return. It is known to use a transistor whose base is connected to the RC network and is conductive during the rise time of the sawtooth edge. Since the base current drawn by the transistor also changes with changes in temperature, there is also a change in the charging current for the clock time capacitor as a function of the temperature through the conductive transistor. As a result, there is an undesirable temperature dependency for the repetition frequency of the sawtooth oscillator. Circuit configurations are also known in which transistors connected to the clock timing capacitor are used during the

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on the flank of the sawtooth, i.e. H. during further claims.

- μ- "time, conductive and a frequency-dependent one built according to the features of the invention

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^kelt . ? " ^B capacitor-switched charging circuit for the fre-

^For special applications, it is desirable to determine the sequence. At the common connection

that the sawtooth oscillator in an integrated form point between the charging circuit and the cycle time

^We / nem semiconductor die together with several capacitor is a comparator with its first

H en circuits are designed monolithically. Connected to the control connection, whereas the second

ih applications as they are for the horizontal control connection of the comparator at the output

^S »° K. nk ^ vstem of television receivers use _I0 terminal of a circuit to determine a switching

r α , phase detectors and driver can also set a threshold value. The output of the comparator

f to be included in the circuit. Both gate is connected to the control terminal of this circuit

5inTten as well as the size of a socket for the definition of the switchable threshold value and with

u take ihiPitero platelets depending on a normally non-conductive discharge circuit

nlr increasing number of required connecting lines, ₅ connected. This discharge circuit is between the

η to Since it is, however, desirable to use this clock time capacitor and the reference voltage ni-

Keeping ISn as small as possible is intended for a high-quality power supply.

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λ ^g Seaue control signal may be required, whereby an to define a switchable threshold value e.ne

ί JdI discrete for frequency determination ₂₀ high threshold voltage on the second control input

^dl f! integrated circuit provided on the end of the comparator, which consists of a differential

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for these applications clock time capacitor connected D; erenzversta.

are connectable. Acquaintance is stronger, u

Eren for these applications the clock time capacitor connected D; e

two connections to which the frequency bucket is kept in the non-conductive state. Are connected as Rolge, ^ Menden elements, and a _25, the comparator provides a first Steuers.gnal.

SerenAnscMustFor the power supply. In addition, the active elements of the discharge circuit as well

holds ir _d ese sTgezaLöszillatoren Schaltungsauf- in their non-conducting state. D, e Ladescha drove

u complex in order to supply the clock generator with electricity in a monolithically integrated form, which this is fed to ad

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solved that a circuit for establishing a ^^ ³ '. ^^ "Vohen threshold value determining

switchable threshold value a first electronic ₅ o ^^ ° J ^. ° ^ "^ \ m The oscillator circuit

Switching element includes that with its control ^S P ^ ^u "f ™ _n X _n 7erf _or d _e rt only two potentials for

end at the output of the comparator and with ^ ^{measured the Er} [Jf ₁ ^ J ""? "" a connection for

its output to the second control connection of the tensioning iver-orgung _{Da a} " _{e active}

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determining tension from a high value to ₅₅ £ ^l £ ™ ™

a lower value depending on the f ^ S ^^ ffen time portion of a periodic

Control signals applied to the comparator to switch, are conductive, the « ^en J ^r _{d the electrical} en

that a discharge circuit for the T.ktze.tkonden »ior ^^^ Äente depending on the

comprises a second electronic switching element, there. ^ "* ^C " J "' ^en ° detrimental to the frequency of the

with a connection to the cycle time _{capacitor 6o} Tempera ur kaun ^^ nachte j _die ^ ^

d Ahlß d Osz IU ors ^ ^effective

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with a connection to the cycle time _{capacitor 6o} Tempera ur kaun ^^ nac j _die ^ ^

is coupled to another terminal at the Osz IU ors ^ ^{effect ve} _{'associated active} elements n second voltage supply line harbors, whereas Tate "Aondensatwj saturation state, whereby the control terminal during ^the ^ ^nt to the output of the _{comparator; Change of} the characteristic and the control connection of the first electronic ^ ♦ ^^ X ^ lbenfaHs to a minimum

bd t and that the discharge 6 ₅ see ^ _n look _{jh i}

and the control connection of the_ first electronic ^^^ X ^ lbenfaHs on a mini

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circuit as a function of the control signal printed here w £ ^ _the V ₀ M _11n J

l ^ S ^ Zti ^^^^^ S ^ chaufgebautistund very slightly monohothic

integrated circuit form can be performed. The frequency of the oscillator output signal can be changed with Can easily be adjusted with the help of an external current applied to the clock time capacitor, whereby a monolithic phase pulling loop or phase blocking loop including a phase detector finds, which causes the oscillator a certain DC voltage at the output of the phase detector triggers.

The advantages and features of the invention also emerge from the following description of a Embodiment in conjunction with the claims and the drawing. It shows

Figure 1 is a block diagram of a monolithic circuit of the horizontal deflection system for a Television receiver in which a sawtooth oscillator according to the invention is used,

F i g. 2 the circuit diagram of the sawtooth oscillator,

3 shows a cycle of the recurring sawtooth oscillation at the output terminal of the oscillator according to Fig.2.

The in Fig. The horizontal deflection system 10 shown in FIG. 1 for a television receiver includes a phase detector 14. an oscillator 16 and a pre-driver stage 18, which within a dashed block 12 are shown and can be made in monolithic integrated circuit form. A low pass filter 20 is between the output 22 of the phase detector 12 and a control connection 24 of the oscillator 16 connected, which is also connected to a clock generator 26 at the control terminal 24. The low pass filter 20 and the clock 26 may be constructed from discrete circuit components that take on values that are less suitable for a monolithically integrated design, and since these circuit components behave relatively stable depending on the temperature. A driver stage 28 and a Output stage 30 are between the output of the pre-driver stage 18 and a flyback transformer 32. The input 34 of the phase detector 14 is with the demodulated horizontal synchronization signals acted upon The flyback transformer 32 is also connected to the input 36 of the phase detector 14, so that the phase of a portion of the flyback pulse with the phase of the horizontal sync signal can be compared.

In operation, the clock of the sawtooth signal at the output of the sawtooth oscillator 16 is via one of the Phase detector 14 generated control signal with the horizontal synchronization pulses phase-coupled The synchronization pulses derived from the composite video signal by an isolating circuit (not shown) are, as mentioned, fed to the input 34 of the phase detector 14 Rücklaufimpuises is a second input 36 of this Phase detector fed to the output side a corresponding direct current signal as a control signal in Depending on the phase difference, if such a between the synchronization signal and the Return pulse exists. This direct current control signal is passed through the low-pass filter 20 to the control terminal 24 of the oscillator to adjust the phase of the periodic output signal of the oscillator. The configuration of the phase detector 14 makes it necessary that a further level of DC current with a predetermined amplitude is generated by the oscillator 16 at the output 22 of the phase detector.

In Fig. 2 shows the circuit diagram of the oscillator 16 as well as the low-pass filter 20 and the clock generator 26. A supply line 40 has a positive supply voltage applied to it and is set DC potential with a first positive amplitude available, whereas a more negative reference potential on the line 42, preferably in the form of Ground potential is available. These lines 40 and 42 can be known as metallization strips Way on the semiconductor die. Of the

ίο oscillator 16 comprises two differentially switched switchable Transistors 44 and 46. The transistor 47 serving as a current source has its collector connected to the Emitter of the transistors 44 and 46 connected, while the emitter of this transistor 47 has a

i _S resistor 50 is connected to the line to which the reference potential is applied. The collector of the transistor 46 is connected directly to the positive supply line 40, while the collector of the transistor 44 is connected to the positive supply line 40 via a resistor 51. At the same time, the base of an inverting transistor 52 is connected to the collector of the transistor 44. The emitter of the transistor 52 is directly on the supply line 40. The transistors 44, 46, 47 and 52 work together with the resistors 50 and 51 as a comparator with an unbalanced output at the collector of the transistor 52, while the input of the comparator from the base of the Transistor 44 and the base of transistor 46 is formed.

The collector of the reversing transistor 52 is connected to the base of a discharge transistor 54 for the clock time capacitor on the one hand and with the base of a switching transistor 56 for the threshold voltage on the other hand tied together. The collector of the discharge transistor 54 is connected to the control terminal 24, whereas be Emitter is connected to the negative supply line 42. A cut-off resistor 57 connects the base of the Transistor 54 and the collector of transistor 52 to the negative supply line 42, whereby a Discharge path for the boundary layer capacitance is created, which enables rapid switching of this Transistors much favored. Between the Koiiektor of the switching transistor 56 and the base of the A resistor 58 is connected to the transistor 46. The resistors 57 and 86 work with the discharge transistor 54 together and form part of the capacitor discharge circuit.

Between the positive supply line 40 and the negative supply line 42, there is a voltage divider composed of a series circuit of the resistors 60, 62, the common connection point of which is at the base of the transistor 46. The values of the resistors 60 and 62 are selected so that a given part of the total supply voltage is effective at the base of the transistor 46 in order to generate a higher threshold voltage Vm , which also determines the maximum amplitude of the sawtooth signal on the output side. The resistors 58, 60 and 62 act with the transistor 56 in such a way that a circuit for establishing the switchable threshold value is created.

Diodes 64 and 66 in series with a Zener diode 6f are located between the positive supply line 4 ( and the negative supply line 42 to increase the amplitude of the supply voltage between the to keep both supply lines 40 and 42 practically constant in a known manner. The temperature coefficients of the diodes 64 and 66 are selected

that they match the temperature coefficient of the Zener diode 68 compensate for a substantially constant and temperature-independent supply voltage to ensure. Between the base of the transistor 47 and the supply line 40 there is a resistor 70, whereas the base of transistor 47 via a diode 72 and a resistor 74 on the negative supply line 42 lies. The series connection of the diode 72 with the resistor 74 causes an essentially constant base-emitter voltage for the transistor 47, so that accordingly a substantially constant Current can be drawn through this transistor from one of the two transistors 44 and 46. Between the connection for the positive supply voltage and the supply line 40 is connected to a resistor 75, which can be designed in the form of a discrete resistor and limits the amplitude of the current, which flows through the diodes 64 and 66 serving for voltage stabilization and the Zener diode 68. When the base voltage of transistor 44 is more positive than the base voltage of transistor 46, the Transistor 44 conductive and transistor 46 non-conductive, so that the entire current from the as a current source effective transistor 47 flows through transistor 44.

A resistor 76 for setting the cycle time, which can be variable, lies with its one Side on the positive supply line 40 and with its other side on the control terminal 24 and on the one side of the clock time capacitor 78, the other side on the reference potential of the negative Supply line lies. The resistor 76 is in the charging circuit of the clock time capacitor 78.

In the free-running operation of the oscillator 16, it controls the charging and discharging of the clock time capacitor 78, whereby a signal with a recurring waveform is available at the control terminal 24, which in the present case is a sawtooth wave 80 according to FIG. 3 is. The time is plotted on the abscissa 82 and the amplitude is plotted on the ordinate 84, which is formed on the clock time capacitor 78 during a functional cycle. At the point in time T0, the capacitor 78 begins to be charged by a current conducted via the resistor 76, as a result of which the rising part 85 of the waveform 80 arises. Also at time TO, transistor 46 becomes conductive and transistor 44 non-conductive. The transistor 46 is made conductive on account of the high threshold voltage Vth, which is effective at the base via the voltage divider from the resistors 60 and 62. The transistor 44 is non-conductive since its base voltage is less positive than the voltage at the base of the transistor 46. The collector voltage of the non-conductive transistor 44 reaches an amplitude value which corresponds to the positive supply voltage on the supply line 40 5s. The transistor 52 is thus non-conductive and does not carry a sufficient base current to make either the discharge transistor 54 or the switching transistor 56 conductive. The negative voltage at the collector of the transistor 52 represents a first control voltage which ensures that the discharge transistor 54 is non-conductive in the time interval T0 to Tl. Thus, the positive supply voltage acting on the supply line 40 charges the clock time capacitor 78 until the point in time TI is reached, at which the voltage at the control terminal 24 and at the base of the transistor 44 is slightly higher than the threshold voltage Vth, which is at the base of the transistor 46 works.

At the time T1, the transistor 44 becomes conductive as a function of the amplitude of the voltage effective at the clock time capacitor 78, since this amplitude exceeds the value of the voltage at the base of the transistor 46. It follows from this that the transistor 44 becomes conductive during the time T1 and T2 and from the transistor 47, which serves as a current source. Current draws, with which the transistor 46 switches to the non-conductive state. As soon as the transistor 44 is conductive, its collector voltage drops and makes the transistor 52 non-conductive. The collector current and the positive collector voltage of the transistor 52 represent a second control signal which supplies the base current to the discharge transistor 54 and the switching transistor 56 in order to make them conductive. The conductive switching transistor 56 connects the resistor 58 in parallel with the resistor 62. As a result, the resistance between the base of the transistor 64 and the negative supply line 42 decreases, which also lowers the voltage which defines the threshold value and is effective at the base of the transistor 46 , this voltage being the lower in FIG. 3 assumes the value Vtl shown.

Also beginning with the time T1 and depending on the second control voltage, the current path running from the clock time capacitor 78 to ground via the transistor 54 and the resistor 86 is closed. Since the resistor 68 has a smaller value, e.g. B. 430 ohms. than resistor 76, e.g. B. 10,000 ohms, the discharge of the clock time capacitor 78 takes place much faster than the charging. This discharge runs exponentially in accordance with the trailing edge section 87 of the waveform 80 according to FIG. 3. The amplitude of the voltage on the capacitor 78 falls until the time T2, at which it is slightly below the lower threshold voltage Vtl that is formed at the base of the transistor 46. As a result, transistor 46 is rendered conductive and transistor 44 non-conductive at time T2, whereby a new cycle of waveform 80 begins, as indicated by part 88 in FIG. 3 is indicated.

Since transistor 44 is made non-conductive again at time T2, it again supplies the first control signal which makes transistors 52, 54 and 56 non-conductive. As a result of this, the resistor 58 no longer acts in parallel with the resistor 62, so that the upper threshold voltage Vth is effective at the base of the transistor 46 again.

The frequency of the freely oscillating oscillator is thus determined by the values of the discrete /? C circuit. the capacitor 78 and the resistor 7t set by selecting the size accordingly of the resistor 76 and the clock time capacitor 7i, the oscillator 16 can be operated over a wide range set the frequency range. Many combinations of values for resistor 76 and capacitor 78 are possible A frequency setting of 15.734 kHz or a corresponding frequency for the horizontal oscillato of a television receiver. The oscillator frequency is ii to a large extent independent of changes in the supply voltage, which are generated by the diodes 64 to 66 and the Zener diode 68 can not be eliminated, since the charging current for the capacitor as well The setting of the lower and upper threshold voltages also corresponds to the changes in the Versoi voltage follow. The oscillator 16 requires nu

509544/39

9 10

A supply voltage with a positive and gate thus depends directly on the charging and discharging time of a negative potential, which is preferably a ground constant as indicated by the resistance values, instead of three different potentials, 76 and 86 and des Capacitor 78 can be defined as in previously known oscillator circuits. The diffused resistor 86 can have the effect of a; required are. This advantage arises from the 5 slightly negative temperature coefficient from the use of the transistor 54 and the transistor 56, which, however, by shortening the time required for switching the threshold voltage and the discharge time of the clock time capacitor, i.e. by connecting these transistors to the reference voltage between line 71 and voltage level or ground instead of another according to FIG. 3 is reduced to a minimum, positive stress levels. 10 The frequency of the oscillator 16 is determined by a

It is important that the free-running oscillator 16 adjusts its control current, which is not generated by the phase detector H frequency as a function of the temperature and changes via the low-pass filter 20 of the semiconductor chip on which it is either supplied or in front of the clock time capacitor. That both transistors and diffusion are derived from this. If the frequency increase produced resistors _{must be temperature-dependent electrical I5} , the clock time capacitor 78 Stroir see properties, is well known. So fed, and when the frequency tends to be decreased e.g. B. the base-emitter voltage, which must be, is from the clock capacitor current is agile to derive a phase detector in a bipolar transistor. The low-pass filter 2C to trigger certain base or collector current, with comprises a resistor 94, which decrease between the increasing temperature. In the time span 20 output 22 of the phase detector and the control period between 70 and 71, which is approximately in the end 24. Furthermore, a capacitor 96 and a magnitude of 95% of the total period resistor 98 are provided, which is in series the output 22 of the sawtooth voltage according to FIG associate. Connected via resistor 94, non-conductive. Changes ₂₅ , the control current flows between the phase detector 14 of the electrical parameters of these transistors and the clock time capacitor 78 of the oscillator unc, depending on the temperature, does not significantly affect the impedance at the output of the phase end negative influences on the charge of the clock time capacitor. Furthermore, the resistors 94 and 98 and sators 78. Although the transistor 54 integrates the oscillator output signal during the discharge time between the times 71 and 72 with 30, so that a direct current level is connected to the clock time capacitor 78, output 22 arises that becomes necessary to actively change the temperature no essential elements of the phase detector 14 within their; Influence on the frequency, since this transistor 54 is to be kept in the active operating range. Operated by enlarging saturation state. The same applies to the resistance value of the resistor 94 changes the transistor 56, so that no undesirable influences flowing from the control terminal 24 to the phase detector on the amplitude of the lower threshold current, the voltage at the output of the phase detector! voltage occur. by an amount that is sufficient to reduce the phase detection

Another temperature-dependent effect relates to driving into saturation and thus the frequency range is to keep the charge storage in the saturated of the system within the intended limits transistors 54 and 56. If at time 72 the 40 this is especially when using the sawtooth decreasing voltage the value Vtl reached, the zillators are required in television receivers in order not to instantly prevent transistors 52, 54 and 56 from making extreme deviations in frequency non-conductive due to these in the limit values damaging output-side power stages. Stratified capacity stored charge. An oscillator circuit that has been successfully tested and the falling edge produced in monolithically integrated circuit form for a short period of time 45 after time 72 thus tends to fall further. This could be achieved with the following components, the duration depends on the temperature, as this is particularly advantageous.

Storage times of transistors 54 and 56 depending on -

tend to rise from the temperature and the resistances are resistance

Time constants of the transistors with increasing 5 ° ^values

Increase in temperature. By switching off the. , _η " _ηηΛ ,

Resistors 51 and 57 refer to this effect as 50 ^ S ™

Charge dissipation within the transistors for reference number 51 3.3 K oohm

Time 72 reduced to a minimum value S ^ SS ™ « A £ ^! 1 °° ^

The repetition frequency thus tends to be 58 \ ₂ Ki oohm from the 55 reference sign

Oscillator 16 generated sawtooth oscillation inde- pendently Referenzze.chen 62 3.6 K.loohm

gig of temperature fluctuations more constant to 1 ™ * ΤΪ? Il T ^ Γ κ

remain, as is the case with KC oscillators, at reference number 70 3.8 Ki oohm

which conductive transistors with the Taktzeitkondensa- Referenzze.chen 60 2.4 K.loohm

tor during the largest part of each period 60 reference numerals 86 430.0 ohms

are connected. The operating frequency of the oscillator 16 A capacitance was used as the clock time capacitor 78

changes with the logarithm of the ratio of 0.01 mF and a resistance mii as resistance 76

of resistors 58, 60 and 62. Therefore when the 10 kilo ohms were used these two elements were used

Resistors are manufactured in such a way that they can be used as discrete circuit elements outside the inte

Relation to one another provided as a function of the temperature 65 integrated circuit. The specified value «

rature remains constant, they practically produce servants for the sawtooth oscillator according to the invention

no frequency change whatsoever as a function of merely the exemplary explanation and not de.

Temperature fluctuations. The frequency of the oscillator limitation of the subject of the invention.

1 sheet of drawings

Claims (4)

Patent claims: 1. Oscillator circuit with one between a first and a second voltage supply line i> i Series to a charging resistor connected cycle time capacitor and a comparator, which with a first control connection is connected to the clock time capacitor and connected to its second control connection a threshold voltage is applied to a control signal on the output side as a function of of the voltage at the clock time capacitor when a certain level is reached, characterized in that a circuit a first electronic switching element (56) to define a switchable threshold value includes, which is with its control terminal at the output of the! Comparator and with its output on the second control connection of the comparator is connected in order to determine the threshold value Tension from a high value to a lower who «depending on the Comparator applied control signals to switch that a discharge circuit for the clock time capacitor a second electronic switching element (54) which has a connection to the Clock time capacitor (78) is coupled and is connected to another connection on the second voltage supply line (42), whereas the control connection with the output of the comparator and the control connection of the first electronic Switching element (56) is connected, and that the discharge circuit as a function of the control signal discharges the cycle time capacitor. 2. oscillator circuit n & ch claim 1, characterized in that the second electronic Switching element consists of a transistor, which is saturated by the control signal is controlled. 3. Oscillator circuit according to claim 1 or 2, characterized in that the circuit for Determination of a switchable threshold value further comprises a first resistor (60) which between the first voltage supply line (40) and the second control terminal of the comparator lies that a second resistor (62) between the second control terminal of the comparator and the second voltage supply line (42) is arranged that a third resistor (58) in series to the first electronic switching element (56) and between the second control terminal of the Comparator and the second voltage supply line is connected, the control terminal of the first electronic switching element is at the output of the comparator. 4. Oscillator circuit according to one or more of claims 1 to 3, characterized in that the charging resistor (76) connected in series with the cycle time capacitor (78) can be changed, and that the frequency of the oscillator circuit can be adjusted by changing the charging resistor.